1. Field of the Invention
This invention is generally directed to a method and apparatus for bringing a component into register with a support with a high degree of precision. More particularly this invention relates to the precise alignment of an electronic chip on a supporting structure.
2. Description of Related Art
Considerable effort has been directed to developing methods and apparatus for precisely positioning one component, such as an electronic chip, on a second component, such as a supporting structure or substrate of any of diverse forms. In accordance with one prior art approach, a robotic device includes a video system to bring bonding pads on a semiconductor device, as the one component or piece, into registration with leads on a substrate as a supporting structure as a second component or piece. Basically, the video system images features on each of the component and supporting structure when they are at locations remote from a work station at which they will actually be joined. If a control system xe2x80x9cknowsxe2x80x9d the position of the robotic device when each video image is produced and the position of each feature on the component with respect to the position of the supporting structure, calculations can then be made to determine a vector over which one of the components must traverse relative to the other component to be in register. After the traversal is complete, the robotic device brings the two pieces into contact, generally by displacing the semiconductor device to the substrate. In addition to robotic systems manufactured by the assignee of this invention, there are a number of variations on this method and apparatus that are exemplified in the following patents:
U.S. Pat. No. 3,923,584 to Hojo et al. (1975) discloses one such positioning arrangement for providing a face down bonder. The surfaces of the two components to be mated together in registration are established as opposed surfaces; the component positions are adjustable horizontally and vertically. A compound prism comprises a truncated quadrangular right prism with a 45xc2x0 truncation and a rectangular prism that form a parallelopiped with a half-silvered mirror film at a common interface and with a total reflecting mirror film at a vertical surface of the rectangular prism. When the two components are spaced apart, the prism is interposed between them to allow images to be taken of the two components. Once the images are taken, the optical mechanism is removed, so the two components can be brought together.
U.S. Pat. No. 4,404,741 (1983) to Lebet et al. discloses an alignment device that includes a gripping device for carrying a part over a substrate. An optical device in the form of a microscope or television camera apparently monitors external housing features in order to assure proper alignment.
U.S. Pat. No. 4,526,646 (1983) to Suzuki et al. discloses an inner lead bonder in which a die is fed along a path. It first is positioned at a die defect camera that enables the removal of defective dies. Next a die positional pattern detecting camera images the die at one location. A lead positional pattern detecting camera monitors the positional pattern of leads on a carrier tape. Once these images have been processed, appropriate alignment is made based upon the information in the images produced by the later two cameras.
U.S. Pat. No. 4,657,170 (1987) to Mxc3xcller discloses a process for bonding an electric component to a connecting tag block in a machine and tape for carrying out the process. An optical instrument 44 is located above a supporting table at which assembly occurs. This enables an operator to see the tape as well as one integrated circuit positioned on the table to determine whether the integrated circuit is properly aligned with the tape. Adjustment of the position is then allowed.
U.S. Pat. No. 4,671,446 (1987) to Sherman discloses a method and system for automatically bonding a lead wire on a semiconductor. In accordance with this method, a contact carrying surface is illuminated at the Brewster""s angle with a beam of light rays having a wavelength in the range of the light transmission coefficient of the semiconductor material constituting the chip. Either the illuminating beam or the reflected beam or both are polarized to produce a difference in intensity of the light reflected from the contact and the light reflected from the semiconductor area. The illuminating light passes through a filter to render to a narrow frequency beam of light rays. The result is enhanced contrast in the reflected beam that is more readily digitized for providing inputs to positioning equipment.
U.S. Pat. No. 4,899,921 (1990) to Bendat et al. discloses alignment apparatus in which an optical probe is intermediate a chip and a substrate. The probe illuminates both the counterfacing surfaces of both the chip and substrate and combines the two images into a single image. After the alignment is correct, the probe is withdrawn to allow the chip to be mounted on the substrate.
U.S. Pat. No. 4,980,971 (1991) to Bartschat et al. discloses a system for precisely placing a semiconductor chip on a substrate. A robotic arm with a gripper separately picks up the chip and the substrate. A first television camera, carried by the robotic arm, captures the image of the substrate to locate a pair of datum points. A second camera, that is stationary with respect to the robotic arm, captures the image of the chip when engaged by the robot to locate another pair of datum points. A machine vision system processes the output signals of both cameras to establish the precise location of the datum points on each of the substrate and chip. This controls the robotic arm to cause the gripper to place the chip on the substrate at a precise location.
U.S. Pat. No. 5,195,234 (1993) to Pine et al. discloses a method and apparatus for visual alignment of parts that includes a device, such as a robotic arm, for picking and placing a part on an object. One device moves and removes optics into and out of a work envelope that contains the object. Another device utilizes information from the optics device for locating landmarks on the object within the work envelope thereby to allow alignment of the part with the landmark in the work envelope. After the optics are removed, the two components are displaced relative to each and into contact.
U.S. Pat. No. 5,523,586 (1996) to Sakurai discloses a burn-in socket used in a burn-in test for semiconductor chips that includes a transparent cover member. The cover member is constituted by fixing an inexpensive TAB tape, which can be finally processed, to a transparent member of glass or other transparent material. The chip electrodes of a semiconductor chip to be tested are set in the recess of the chip container and electrically connect to internal electrodes of the chip container by use of leads on the TAB tape. The alignment of the leads, chip electrodes and internal electrodes is facilitated by viewing through the TAB tape from the cover member by video or other means.
U.S. Pat. No. 5,590,456 (1997) to Armington et al. discloses an apparatus for precisely aligning and placing optoelectric components on a substrate. A single camera looks through a transparent alignment tool that holds the component to the substrate below it thus allowing both the component and the substrate to be seen together by the camera. The alignment tool and substrate are adjusted to align the two precisely and then are brought together while being seen by the camera. If the optoelectric component is a laser chip, the chip can be energized while on the glass alignment tool to produce a laser spot that is superimposed on the visible light image via a series of lenses and mirrors.
There now exists a new class of electronic chip-substrate combinations called chip scale packages. The counterfacing surfaces of the chip and substrate carry bonding pads and terminals respectively. The bonding pads are typically about 4 mils square; the leads have a cross section of about 2 mils. In order to assure appropriate placement, the robotic device must align the components to within less than xc2x11 mil, typically within a tolerance of less than 10 microns.
Each of the foregoing approaches, with the exception of the Armington et al. patent, displaces one component relative to the other after visual images related to their positions have been determined. This relative motion comprises lateral and vertical components and generally involves a significant displacement. Achieving placement accuracies in the ten-micron range while maintaining acceptable rates of operation taxes or exceeds the capabilities of these robotic devices. Moreover, at this requirement for precision changes in temperature require elaborate and time-consuming calibration procedures that further degrade operating speed. As a consequence alternate or supplemental procedures have been suggested to enhance the positioning processes. For example, U.S. Pat. No. 5,518,964 (1996) to DiStefano et al., discloses a microelectronic connection component that is positioned with the leads faced down toward a substrate and onto terminals connected to the substrate in a Z or S fashion.
U.S. Pat. No. 5,348,214 (1994) to Nishiguchi et al. discloses a method of mounting a plurality of semiconductor elements each having bump electrodes on a wiring board by pressing the semiconductor elements to the wiring board while aligning the electrodes and then heating the structure. Any misalignment in the initial positioning of the chip with the board apparently is corrected provided the bump electrodes lie somewhere in the concavity of the electrodes on the wiring board.
U.S. Pat. No. 5,092,033 (1992) to Nishiguchi et al. discloses an alternative approach whereby the steps of electrically connecting at least one pair of bumps on a semiconductor device includes bringing the bumps into contact with a surface of the packaging substrate. The semiconductor device is moved relative to the packaging substrate while monitoring whether electrode terminals formed on the surface of the packaging substrate in at least one pair are electrically connected to each other. Stated differently, a pair of electrodes on the packaging device or different pairs of electrodes on the packaging device may be energized for alignment with interconnected bumps on the semiconductor device. Thus the system will monitor the current flow between the devices when the corresponding pairs of bumps and electrodes are in register.
U.S. Pat. No. 5,212,880 (1993) to Nishiguchi et al. discloses still another alternative in which an optical device is located between the flip chip and the substrate. Coherent light irradiates the bonding head and substrate and light reflected by the bonding head and substrate form interference patterns. The inclination of the bonding head against the substrate is performed by observation of interference fringes caused by the interference between the light reflected from the bonding head and light reflected by the substrate. The disappearance of the interference fringes indicates that the bonding head and the substrate are in exact parallel relationship.
The foregoing patents thereby disclose a number of alternative or supplemental approaches for enhancing the alignment capabilities of prior art assembly apparatus. In accordance with these patents conventional assembly apparatus provides an initial alignment. Final alignment is achieved mechanically, as when bumps on the chip drop into concavities on the wiring board, or electrically, as monitoring different pairs of leads to determine when appropriate conductive paths are established. Each approach increases the time to position and attach a chip to a substrate. This can produce a significant reduction in production rates. The alternative of increasing the inherent accuracy of the robotic devices will increase the costs of such devices to prohibitive levels. What is needed is an apparatus and method that, at a reasonable cost, enable conventional robotic apparatus to achieve the required enhanced positioning accuracy without any significant decrease in production rates, without any significant increase in apparatus costs and with independence of any environmental conditions.
Therefore it is an object of this invention to provide a method and apparatus for enabling the precise alignment of a component on a supporting structure.
Another object of this invention is to provide a method and apparatus for precisely locating electrical terminals on a supporting structure with bonding pads on an electronic chip.
Still another object of this invention is to provide a method and apparatus particularly adapted for the automated assembly of an electronic chip on a supporting film during the production of a chip scale package.
Still another object of this invention is to provide a method and apparatus for enhancing the capability of conventional assembly apparatus to perform precise positioning of an electronic chip on a supporting structure in an automated manufacturing apparatus with an insignificant impact on production rates.
In accordance with one aspect of this invention, a first component with at least one alignment feature on one surface thereof and a second component with at least one alignment feature at an area of transparency therethrough are brought into a proximate spaced position such that a superposed image of corresponding alignment features on the components can be generated in response to light reflected from the first component. The superimposed image is then analyzed to generate alignment signals that enable final registration of the first and second components.
In accordance with another aspect of this invention, first and second supports positioning first and second components, each having alignment features, maintain the second component at a reference plane while the first support locates the first component proximally to the second component on one side of the reference plane. An image generator having a given depth of field characteristic images the alignment features from the other side of the reference plane when the alignment features are within the depth of field of the image generator. An optical path directs an enlarged image to a location where portions of the enlarged image are converted into electronic video signals that enable the first and second component to be brought into contact in precise registration.
In accordance with still another aspect of this invention, an apparatus for positioning an electronic chip having bonding pads on a planar surface thereof on a substrate with leads formed thereon in transparent areas thereof. A robotic device carries the electronic chip for movement in an x-y horizontal plane and along and about a Z axis perpendicular to the x-y plane. A substrate support maintains the substrate in a horizontal plane. A real time imager generates simultaneously first and second enlarged images of first and second spaced predetermined portions of the substrate and the chip based upon light reflected from the chip. A processor generates alignment signals in response to the first and second enlarged images. A control, that initially aligns the chip and substrate in a closely spaced relation, performs a final alignment in response to the alignment signals and then moves the electronic chip along the Z axis into contact with the substrate thereby to mount the electronic chip to the substrate.